A 35-year-old Iraqi man - questioned in February following a tip off - was released without charge after it was established he was not in France on the day of the killings.

Another 48-year-old man arrested in February was also released from custody after investigators found no direct link between him and the killings.

The bodies of Iraqi-born Mr Al-Hilli and his dentist wife were discovered along with that of Mrs Al-Hilli's mother in their BMW on a remote forest route by cyclist Brett Martin.

The couple's two young daughters survived the attack, while local man Mr Mollier was also murdered.

A spokesman for Surrey Police said it was "continuing to provide support" to the French investigation.

He added: "As part of the Joint Investigation Team (JIT), which was established following the deaths, officers from the Surrey and Sussex Major Crime Team have worked closely with the French authorities to progress a number of lines of inquiry in the UK.

"This is a complex inquiry, however Surrey Police remains committed to helping find answers to what happened and continuing to assist the French investigation wherever possible."